Hot stamping is an innovative way to manufacture complex-shaped components of high strength steel (HSS) sheet with a minimum of springback, meanwhile, it can also obviously improve the tensile strength of the formed parts.The coupled thermo-mechanical FE model for hot stamping of HSS sheet for the B pillar was established by commercial software Pam-stamp. Dynamic explicit module was used to simulate the forming processes under different process parameters. The effects of process parameters on thinning of the blank were studied, the maximum thinning zones of the blank in hot stamping were analyzed. The results show that the thinning rates of the blank increase when the blank holder force(BHF) and friction coefficient increase, the maximum thinning zones appear at the straight wall and corner of the B pillar. The causal of blank thinning during hot stamping was analyzed. Experiments had been conducted with the process parameters obtained by simulation. The experimental and simulation results were in good agreement.